It is known, for example, that the gas oils used for automobile, naval and aeronautical internal combustion engine feeding or for heat generation purposes, become less fluid with decreasing temperature. This causes serious drawbacks in their use.
Such a phenomenon is mainly due to the precipitation of n-paraffins contained in the gas oil.
It is also known to obviate such a drawback by adding suitable substances, generally of polymeric type to the above said liquid hydrocarbons from refining.
The additives commonly used for such a purpose are represented by:
ethylene-vinyl acetate copolymers having suitable molecular weight values and compositions, as disclosed, for example, by U.S. Pat. Nos. 3,048,479; 3,087,894; 3,093,623; 3,126,364; 3,159,608; 3,250,714; 3,627,839; etc.;
oil-soluble polymeric N-aliphatic acrylamides having a molecular weight of at least 1,000 in which the aliphatic groups contain an open chain of at least 8 C with not more than 2 are atoms of oxygen or sulfur and the rest are carbon atoms, as disclosed by U.S. Pat. No. 2,387,501;
ethylene-propylene-(non-conjugated diene) copolymers or terpolymers, prepared with homogeneous-phase catalysts (based on vanadium compound and organometallic aluminum compounds), as disclosed by Italian Patent Nos. 811,873 and 866,519;
ethylene-propylene-conjugated or non-conjugated diene terpolymers, which are prepared with homogeneous-phase catalysts and are subsequently degraded by thermooxidation until suitable values of molecular weight are reached, as disclosed by U.S. Pat. Nos. 3,374,073 and 3,756,954.
All the above additives are satisfactory from the standpoint of lowering the pour point of the liquid hydrocarbons and in some cases the cloud point (C.P.) too, namely the temperature value at which the first paraffin crystals appear. But they do not sufficiently control the crystallization kinetics and the size and the shape of the paraffin crystals occurring by cooling.